1. Electrical Heat Tracing Control & Monitoring Basics
Richard H. Hulett Ben C. Johnson
Thermon Thermon
San Marcos, TX San Marcos, TX
IEEE IAS/PES Northern Canada Chapter February 2013

2. What This Session Will Cover:
Electrical Heat Tracing (EHT) Control Options
Advantages and Limitations of Each
EHT Monitoring Options
Controls Communications Methods
Energy Management of Large EHT Systems

3. Reflect on an Overview of an Electrical Heat Tracing System
Main Power Transformer
Electrical Distribution Panel
Field Wiring Requirements to Individual Heaters
Heat Trace Power Connection Points
Individual Line Sensing Controllers (Optional) with Dedicated Temperature Sensor (Possible)
Thermal Insulation System

4. Power Distribution / Control Panel Temperature Controller
EHT System Overview…
Transformer
480Vac Primary 120/208Vac
Conduit and Wire
Power Distribution / Control Panel
Temperature Controller
EHT Power Connection
Mount Transformer and Control Panels
Run Conduit and Wire
Install Heat Tracing
Make All Terminations
Install Thermal Insulation
Test and Commission System
Thermal Insulation
Thermal Insulation
Temperature Sensor

5. Basic Components of a Heat Tracing Circuit
1 Circuit Protection/Distribution
2 Power Connection 1 4
3 Heat Tracing Product 2
4 “Hot End” Termination 5
5 Temperature Controller
6 Temperature Sensor 6 3

6. Ground-fault Protection Of Equipment
“A system intended to provide protection of equipment from damaging line-to-ground fault currents by operating to cause a disconnecting means to open all ungrounded conductors of the faulted circuit. This protection is provided at current levels less than those required to protect conductors from damage through the operation of a supply circuit overcurrent device.”
To Alarm
Heating
Cable

7. Reflect on Common Applications
Freeze Protection
(winterization)
Viscosity Control
Prevent Condensation
Frost Heave Prevention

8. Common Control Methods Control Approaches
No Control
Ambient Sensing
Line Sensing
Dead-Leg Control
Four basic approaches to control of an electrical heat tracing system have been used. These include (1) no control, (2) ambient sensing, (3) line sensing, and (4) dead-leg control.
Of these the most common are ambient sensing for freeze protection applications and line sensing for process temperature maintenance applications.
The pros and cons of each will be presented to form a basis on which to introduce the APC concept.

9. No Control S/R Heater Output Power Temperature amb T pipe tmax tmin
No Control (a common option with self-regulating heat trace)
Typically for freeze protection of water and water-based solutions
Pipe temperature determined by thermal equilibrium of self-regulating heater and
line specific heat loss characteristics
Power
Temperature
S/R Heater Output
Tmax
amb
tmin
T pipe
tmax
ambient
tmin
amb

10. No Control Advantages: Limitations: Common Applications:
No Cost for Controls
Reliability of Control System Not an Issue
Limitations:
Wider Temperature Range
Poor Energy Efficiency
Common Applications:
Process Temperature Maintenance Where Ambient Variation is Low
While the “no control” approach is not commonly used in North America, is used frequently for process temperature maintenance of crude oil and fuel oil in equatorial locations. Thermon often finds the competition bidding a S/R heating system with no temperature control.
Later in the presentation you will see the outcome of such an approach.
Note that CompuTrace has a “no control” option. The resulting temperature range, which is based on the input minimum and maximum ambient temperatures is presented in the output data.

11. Mechanical Thermostats
Electrical Heat Trace Control Basics
Mechanical Thermostats
Ambient sensing for ordinary and hazardous (classified) locations
Pipe/tank wall sensing in a variety of temperature and amperage ranges

12. Mechanical Thermostats
On-Off Control or Limiter for a Single Electric Trace Heater
Control Action and Temperature Sensor are Generally in Close Proximity to Heater Being Controlled
Models in "Explosion Proof" Housings or with Hermetically-sealed contacts are Used in Hazardous (Classified) Areas.
Provides Little (if any) Temperature Read-out or Heat Trace Circuit Information
Provides No Communications Capability

13. Common Control Sensing Techniques Control Approaches
No Control
Ambient Sensing
Line Sensing
Dead-Leg Control
Four basic approaches to control of an electrical heat tracing system have been used. These include (1) no control, (2) ambient sensing, (3) line sensing, and (4) dead-leg control.
Of these the most common are ambient sensing for freeze protection applications and line sensing for process temperature maintenance applications.
The pros and cons of each will be presented to form a basis on which to introduce the APC concept.

14. Ambient Sensing Control
“T” Splice
Power Connection

15. Ambient Sensing Control
Ambient Sensing Control is typically a single “On-Off” thermostat which drives a contactor to energize an entire power distribution panel when the ambient temperature falls below the set point of the thermostat. By comparison to “No Control” this saves some energy at a minimal cost adder.
EHT Power
Temperature
S/R Heater Output
tpipe
tmin
amb
100% ON
Off
tambient
setpoint
tambient
setpoint

16. Basic Ambient Sensing Control Panel
Ambient Sensing Thermostat
Main Contactor for Panel Control
Prewired Branch “EPD” Breakers
Lock-Out / Tag-Out Feature
Door-mounted HOA switch and Lights
While the “no control” approach is not commonly used in North America, is used frequently for process temperature maintenance of crude oil and fuel oil in equatorial locations. Thermon often finds the competition bidding a S/R heating system with no temperature control.
Later in the presentation you will see the outcome of such an approach.
Note that CompuTrace has a “no control” option. The resulting temperature range, which is based on the input minimum and maximum ambient temperatures is presented in the output data.

17. Basic Ambient Sensing Control Ambient Sensing
Advantages:
Low Cost for Controls
Reasonable Temperature Range
Limitations:
May not be suitable for Safety Showers
Not Energy Efficient
Common Use:
Winterization/Freeze Protection Applications
Since the early 1970’s, ambient sensing for freeze protection applications has been the primary method of control. The system typically consists of an ambient sensing mechanical thermostat controlling a contactor in a distribution panel. The resulting cost savings when compared to line sensing are based on needing only one thermostat instead on one for each circuit.
When using S/R heating cables, the resulting temperature range is acceptable in most cases except for safety showers. When the worst case conditions for high temperature such as no safety factor, no wind, and thermal resistances between the pipe to insulation and insulation to weather barrier are applied, the equilibrium pipe temperature can exceed the allowable limits for safety showers and eye washes.

18. Common Control Methods Control Approaches
No Control
Ambient Sensing
Line Sensing
Dead-Leg Sensing Control
Four basic approaches to control of an electrical heat tracing system have been used. These include (1) no control, (2) ambient sensing, (3) line sensing, and (4) dead-leg control.
Of these the most common are ambient sensing for freeze protection applications and line sensing for process temperature maintenance applications.
The pros and cons of each will be presented to form a basis on which to introduce the APC concept.

19. Line Sensing Control
End Termination
Power Connections

20. Line Sensing Temperature Control Line Sensing
Advantages:
Tight Temperature Control
Energy Efficient
Limitations:
Higher Cost
Potential Reliability Issues
Common Applications:
Process Temperature Maintenance
Line sensing has been the primary method of control for process temperature heat tracing applications. This has typically been accomplished with mechanical thermostats. Recently, electronic controls with RTD sensors are becoming more widely used for line sensing control.
For applications requiring tight temperature control, line sensing is really the only control option.
From an energy savings standpoint, line sensing is the most efficient control option. For process maintenance applications heat tracing is required only when there is no flow in the pipe. This may be as low and 10% or 20% of the time. A line sensing control system will be energized during the no flow condition. However, other systems such as ambient control approaches do not detect pipe temperature. They will be energized during flow conditions if the ambient temperature or dead-leg temperature is below the set point. Line sensing is the most energy efficient.

21. Common Control Methods Control Approaches
No Control
Ambient Sensing
Line Sensing
Dead-Leg Sensing Control
Four basic approaches to control of an electrical heat tracing system have been used. These include (1) no control, (2) ambient sensing, (3) line sensing, and (4) dead-leg control.
Of these the most common are ambient sensing for freeze protection applications and line sensing for process temperature maintenance applications.
The pros and cons of each will be presented to form a basis on which to introduce the APC concept.

22. Dead-leg Sensing Control
“T” Splices
Power Connection

23. Dead Leg Sensing Control
Advantages:
Fewer Electrical Circuits for Reduced Costs
Reasonably Tight Temp Control
Limitations :
Must Have a Suitable Dead Leg
Heater Selection must allow EHT to be “ON” During Process Temperature Excursions
Temperature Monitoring Very Limited
Common Use:
Complex Piping Process Requiring Line Sensing Temperature Control

24. Control: Dead Leg Sensing
Additional Precautions for Dead Leg Sensing :
Control: Dead Leg Sensing
The actual control band is the same as line- sensing when pipe & insulation conditions are the same
Different pipe sizes being controlled from one “dead leg” may have different temperatures
the representative “dead leg” must be carefully selected
some variation in maintain temperature between different pipe sizes may occur

25. Common Control Modes Control Approaches On-Off Control
Proportional Control
Soft-Start
APC (Ambient Proportional Control)
Four basic approaches to control of an electrical heat tracing system have been used. These include (1) no control, (2) ambient sensing, (3) line sensing, and (4) dead-leg control.
Of these the most common are ambient sensing for freeze protection applications and line sensing for process temperature maintenance applications.
The pros and cons of each will be presented to form a basis on which to introduce the APC concept.

26. Line Sensing Control Power Pipe Temperature tpipe S/R Heater Output
Utilizing one (or more) pipe wall mounted sensors for each heat trace circuit. Provides fairly accurate control of pipe temperature and highest energy savings
tpipe
tmin
amb
S/R Heater Output
tsetpoint
Power
Pipe Temperature
tsetpoint
Control Band
This slide shows equilibrium condition of a S/R heating system for a process temperature maintenance application. The control band with line sensing is typically between 10° F to 20° F. This is represented by the shaded area.
With the steeper control characteristic of APC the control band is not much larger. Note that when the maintenance temperature is much higher than the maximum ambient temperature the power output at the maximum ambient condition may be well above the 20%.
You do not need to know how to calculate the operating temperature band for an APC system. Vendor software will do this for you. Select ambient proportional control in the SETTINGS section. The operating control band is established with the “Op Maint Temp” and the “Op Maint Temp Hi” shown as output.

27. (APC) Ambient Proportional Control
APC (typically a multipoint electronic control system with a single ambient sensor to deliver power proportionally from 100% at the minimum design ambient to 0% at the desired maintain temperature. (Note that 20% is the minimum power delivery to maintain current & earth-leakage current monitoring functions. APC saves energy
by comparison to conventional ambient sensing control.
tpipe
tmin
amb
Heater Power
100% 0%
Tminimum ambient
20% Power
Off
Tambient
setpoint
Ambient Temperature
Tambient
= Maintain Temp

28. Common Monitoring Methods Control Approaches
Voltage (including Continuity) Monitoring
Load Current Monitoring (with Low and High Alarm and Trip)
Earth-leakage Current Monitoring
Temperature Monitoring (with Low and High Alarm and Trip)
Four basic approaches to control of an electrical heat tracing system have been used. These include (1) no control, (2) ambient sensing, (3) line sensing, and (4) dead-leg control.
Of these the most common are ambient sensing for freeze protection applications and line sensing for process temperature maintenance applications.
The pros and cons of each will be presented to form a basis on which to introduce the APC concept.

29. Continuity Monitoring
End-of-Line Lights for Parallel Heat Trace (S/R, Power Limiting, etc.)
…or “Third Wire” Monitoring

30. Trace Heater Electrical Configuration
Series
 V R N H H
Parallel N 30

31. “EPD” Breaker Monitoring
Advantages
Equipment Protection Devices Required per Code
Detects Dielectric Weaknesses in Heaters
No Additional Conductors Required
“T” Splice
Power Connection

32. Ambient Sensing Control with Branch Circuit Breaker Monitoring
Includes:
Ambient Sensing Thermostat
Main Contactor for Panel Control
Prewired Branch “EPD” Breakers
Loss of Voltage Alarm with individual Circuit Alarm Acknowledgement
Automatic Reset when corrected
Lock-Out / Tag-Out Feature
Door-mounted HOA switch and Lights
While the “no control” approach is not commonly used in North America, is used frequently for process temperature maintenance of crude oil and fuel oil in equatorial locations. Thermon often finds the competition bidding a S/R heating system with no temperature control.
Later in the presentation you will see the outcome of such an approach.
Note that CompuTrace has a “no control” option. The resulting temperature range, which is based on the input minimum and maximum ambient temperatures is presented in the output data.

33. Heat Tracing Product Types
Recap:
MI Heat Tracing
Polymer Insulated Heat Tracing
Zone-Type Constant Watt Heat Tracing
Self-Regulating Heat Tracing
Power-Limiting Heat Tracing
Skin Effect Heating System

34. Electrical Heat Tracing Product Types
Positive Temperature Coefficient (PTC) Heat Tracing for Complex Piping
Parallel and Series Constant Wattage Heat Tracing for Interconnecting Piping
Specialty Heat Tracing:
Skin Effect Systems, Tank and Hopper Heating
Self-Regulating
Parallel Constant Watt
MI Constant Watt
Skin Effect Heating
Power-Limiting
Series Constant Watt
Tank Heating
Hopper Heating

35. The Difference in Trace Heater Types
Electrical Configuration
Element Type
Dielectric Insulation

36. Trace Heater Electrical Configuration
Series
 V R N H H
Parallel N 36

37. Heating Element Types

38. Heat Output Power Temperature
Self-Regulating & Power- Limiting Heater Output
Power
Heat loss is proportional to the temperature difference between the pipe and the ambient. On the above graph it is shown as a upward extending line from ambient temperature. Being proportional, if the temperature difference doubles, the heat loss doubles.
Also shown on the graph is a typical S/R heating cable power output.
This system will stabilize where the heat loss line and the power output line intersect. This is the equilibrium temperature. Heat out equals heat in.
Constant Wattage Heater Output
Temperature

39. Multi-Function Control and Monitoring Device
Multi Function Controller
Temperature Sensor
Advantages
Accurate Control with Adjustable Dead Band and different Control Methods
Low and High Temperature Alarms & Trip
Low and High Load Current Alarms & Trip
Adjustable Earth Leakage Alarms & Trip
Circuit Information Displays & Alarms
Remote Communications Capabilities

40. EHT Control & Monitoring Systems
Single Point and Multi-point
Control and Monitoring Units
Permit on-off, proportional and APC control with significant monitoring and communications capabilities
Temperature monitoring and alarms
Provide heating circuit monitoring

41. Advanced Electronic Control
Accurate Temperature Control with Various Programmable Control Methods
Load Current
Ground-leakage Current
Control Options
User Interface
Remote Digital Communication

42. Microprocessor-based Control & Monitoring Panels
Includes:
individual Circuit Alarms for with Acknowledgement
Prewired Branch Breakers (EPD-Type not required if Earth Leakage monitored)
Individual Control Relay per Heater
Swing-out panel provides complete access to :
Lock-Out / Tag-Out Features for Branch Breakers
Current & Ground Leakage Current Transformers
Automatic Reset when corrected
While the “no control” approach is not commonly used in North America, is used frequently for process temperature maintenance of crude oil and fuel oil in equatorial locations. Thermon often finds the competition bidding a S/R heating system with no temperature control.
Later in the presentation you will see the outcome of such an approach.
Note that CompuTrace has a “no control” option. The resulting temperature range, which is based on the input minimum and maximum ambient temperatures is presented in the output data.

43. Temperature Monitoring
Low Temperature Alarm
High Temperature Alarm
Can Use:
Mechanical Thermostat
High Temperature Limit Switch
Electronic Controller with RTD

44. Winterization Prevents:
Ruptured Pipes
Loss of Safety Systems
Interruption of Water Supplies
Plant Outages

45. Control Systems Communications
RS 485 bus with Modbus ASCII protocol
Features
- Temperature, Current and Ground Current Indication and Alarm

46. Control Systems Communications
Includes
Alarm Logs
Alarm Diagnostics

47. Control Systems Communications
Includes
Isometric Drawings

48. Control Systems Communications
Many Communications Systems can now include direct connection to a DCS System…
…and VNC: Virtual Network* Computing
On a shared network an interface can be viewed and controlled * via VNC from a PC, “Tablet” and/or a Smart Phone
Bottom half of back cover.
VNC can be wireless
*As governed by customer’s network restrictions

49. The Most Critical Component of a Heat Tracing System . . .
Isn’t an Electrical Device or Appliance
Is Rarely Considered a Part of the System
Is Regularly Misapplied, Unprotected and Abused
Is the #1 Cause of Low Temperature Problems
What Is It?

50. Thermal Insulation!

51. Questions ?